This invention relates to a membrane press, work base, and method of elevating a three-dimensional workpiece carried by the work base. Membrane presses have been in existence since the early 1900's, and are used for applying a uniform, laminating exterior veneer to the top surface, corners, and peripheral borders of a relatively thin and flat, three-dimensional workpiece. The resulting laminated workpieces are typically used in furniture fronts, doors, cabinetry, desks, and other similar items where pleasing outward appearance and durability is desirable.
The pressing cycle of the present-day membrane press, using combined contact and convection heating, takes place in essentially four stages. The membrane press is first opened, and the laminating foil clamped along its respective edges to a tensioning frame positioned directly above the workpiece to be laminated. The tensioning frame includes a top heating platen and membrane located adjacent to and above the laminating foil. The membrane is sucked upwardly by a vacuum source to the top heating platen which acts to heat the membrane.
In a second stage, the membrane press is closed over the workpiece, and the membrane ventilated through exhaust passages. Hot air is circulated between the top heating platen and membrane to further heat the membrane. The foil is sucked upwardly into contact with the heated membrane by a second vacuum source to change the foil to its plastic state.
Thirdly, a third vacuum source is established under the heated foil to prevent air pockets from forming between the foil and exterior surface of the workpiece. The hot air circulated between the top heating platen and membrane is replaced by pressurized heated air to force the membrane and laminating foil downwardly onto the surface of the workpiece.
Finally, separation air is injected between the foil and membrane to lift and separate the membrane from the foil. After pressing, any excess foil overlapping the peripheral borders and corners of the laminated workpiece is removed by cutting. An additional surface finish or coating may then be applied to the workpiece to create a finished product ready for use in a furniture front, or similar article.
In order to properly and uniformly apply the laminating foil to the peripheral borders and corners of the workpiece, as described above, the workpiece must be slightly elevated above the supporting surface of the press table. According to prior art presses, a relatively thin particle board, often referred to as a dummy board, piggyback board, or raiser panel, is placed under the workpiece. These dummy boards limit the production of the press, since the corners of the boards often crumble during pressing. The crumbled particles then become positioned under the foil, which ultimately results in workpiece rejects as the particles show through the foil. Moreover, the dummy boards must be shaped and sized to fit the dimensions of each particular workpiece.
The present invention provides an alternative means for elevating the workpiece above the supporting surface of a work press, such as a membrane press. The present invention utilizes a fluid force acting beneath the workpiece and foil to elevate the workpiece. This results in increased production of the press, and reduces the number of workpiece rejects.
In addition, the invention in not limited to membrane presses, but instead has application to any work base where elevating a workpiece for processing is desirable. For example, the invention may be applicable to CNC routers, thermal-forming presses, deep-draw machines (vacuum presses), or any machine combining surface and edge processing in a single step.